I am on my 4th pregnancy. I have never gain very much weight with my pregnancies (2 were in my 20's, 2 were in my early 30's), but I gained just a few more pounds with each pregnancy (2-3lbs more each time). If you are underweight, you should gain more and not be concerned if you don't loose the extra afterwards. Likewise, it is suggested that you gain slightly less if you are overweight. A healthy weight does wonders for a developing baby. So does a healthy diet.
I applaud you for working so hard at overcoming your battles before getting pregnant again. Not everyone is willing to work that hard for another person. It shows great strength in you! Just make sure everything you put in your mouth has nutritional value (including beverages) and that you are only eating when hungry, not bored, tired, etc. If you really concentrate on that, you shouldn't gain more than you should be. And stay off the scale at home. Let the ob office do the weighing and close your eyes when they read the scale. ;)
I have been working with some of my own diet-related battles with this pregnancy. I have an extreme love for carbs, sweets and "quick" foods. I don't eat enough fruits and veggies. Honestly, I have to chant "Healthy mommy = healthy baby" over and over again when I am really wanting that unhealthy, non-nutritious food, so that I can replace it with something of nutritional value. My battle is not near as hard as yours........but seeing the strength that you have and the will power to make a change, has actually provided me with more motivation to make my struggle a thing of the past!
You are a good mom! Keep it going!